1. Field of the Invention
The present invention relates to an electricity generation system for an aircraft or the like equipped with a jet engine.
2. Description of the Related Art
Jet engines including a compressor are known as propulsion devices for aircraft and the like. In the aircraft or the like equipped with this type of jet engine, a fuel pump, a hydraulic pump, a lubricant pump and other devices equipped to the jet engine are commonly driven by a rotating high-pressure shaft of the compressor, via an accessory gearbox, while electric power required for the aircraft or the like is commonly supplied from an electric generator driven by the rotating high-pressure shaft of the compressor, via the accessory gearbox. The configuration that the mechanical pumps as well as the electric generator is driven by the high-pressure shaft of the compressor has a problem such that an increase in power consumption in the aircraft or the like increases a load on the high-pressure shaft of the compressor, which leads to reduced surge margin, and thus, increased possibility of surge (see JP 2002-70585 A). Particularly with a great increase in power demand in aircraft and the like in recent years, reduction of surge margin has becoming a problem. Here, the “surge” means a phenomenon that the jet engine does not operate properly due to stall of the compressor or the like. The “surge margin” is a measure of how close an operating point is to surge, and corresponds to a region between the operating line and the surge line on the map of low-pressure compression part entry air flow rate versus pressure ratio of the compressor.
To deal with the above problem, an electricity generation system configured to generate electricity by being driven by both the high-pressure shaft and the low-pressure shaft of the compressor has been proposed (see non-patent document: Christian Zaehringer and two others, “Towards the Powerhouse for More Electric Aircraft Dedicated Engine Concepts”, http://www.mtu.de/en/technologies/engineering_news/development/Zaehringer_Towards_the_Powerhouse_en.pdf, pages 3 to 4, FIG. 2).
The aforementioned non-patent document, however, only discloses the concept of an electricity generation system including electric generators driven by the high-pressure shaft and the low-pressure shaft of the compressor, respectively, to generate electricity. In other words, the aforementioned non-patent document only shows the theoretical possibility of supplying increased power while maintaining the performance, operability and surge margin of the jet engine, provided by configuring an electricity generation system to generate electricity by being driven by both the high-pressure shaft and the low-pressure shaft of the compressor; it hardly discloses how to realize the concept, technically.